The goal of this contract is to provide support of National Toxicology Program (NTP) hazard identification activities targeted toward the prevention of diseases or adverse effects caused by environmental exposure to chemical or physical agents. The specific task of this contract is to procure assistance in preparing the Report on Carcinogens (RoC) and the background documents used in the review of substances under consideration for possible listing and delisting in the RoC (that is candidate substances). The RoC is a congressionally mandated document that lists agents, substances, mixtures or exposure circumstances (here-after referred to as substances) that are known or reasonably anticipated to be human carcinogens. It is a compilation of [unreadable]substance profiles[unreadable], each of which contains a brief description of the carcinogenicity, exposure and regulatory information for a specific substance, for all listed human carcinogens. In 2008, Constella Group provided support to update the information for some of the substance profiles that are currently listed in the 11th Annual Report on Carcinogens (2004) in preparation for the publication of the 12th Annual Report on Carcinogens. There are approximately 200 profiles that need to be updated, so this is an ongoing task. Candidate substances are evaluated by a rigorous review process, consisting of sequential reviews by distinct scientific committees. The review process for the RoC was revised in response to the recently enacted Office of Management and Budget peer review guidelines and the revised process was released in April 2007. Under the revised review process, each background document will be peer review by an expert panel composed of scientists from public and private sectors with relevant expertise and knowledge selected by the NTP in accordance with the Federal Advisory Committee Act and HHS guidelines and regulations. (The expert panel also makes a recommendation for listing in the RoC). The statement of work of the contract was modified to support NTP in providing administrative support for convening the expert panel meetings. In 2008, three expert panel meetings were convened reviewing 5 candidate substances. The background document is the primary scientific resource used for applying the criteria and making a recommendation on listing status of the candidate substance in the RoC. It also serves as a resource that can be used in preparing the substance profile published in the RoC. The background document for a candidate substance presents data on (1) use and production, (2) exposure including from environmental sources, within the general population and in the workplace, and (3) human epidemiology, animal, genotoxicity and mechanistic studies from the publicly available peer-reviewed literature. The background documents are written by Constella Group, NTP Staff or expert consultants. They are reviewed internally before they undergo peer review by the expert panels and are place on the NTP website for public comments (See (http://ntp.niehs.nih.gov/go/29679). Constella provided support for 5 draft background documents that were peer-reviewed in the expert panel meeting mentioned above. Constella also provided support for finalizing the 5 background documents based on the expert panel's peer-review comments, and the documents have been posted on the NTP website. Keywords cancer;hazard identification;congressional mandate;National Toxicology Program;Department of Health and Human Services;exposure;regulations;human cancer studies;animal cancer studies;genotoxicity;biological mechanisms